Black and white images having a high resolution, such as black and white photographs, are growing in popularity. Despite accounting for only a small percentage of the total images produced each year, photographers continue to produce black and white photographs using conventional silver halide techniques. The photographers are also adapting inkjet printing techniques to produce high resolution, black and white images. For instance, black and white images are printed using a color inkjet printer by applying inkjet inks of composite colors on the print medium. The color inkjet printer mixes cyan, magenta, yellow, and black inkjet inks on the print medium to achieve a composite black. To create gray tones, the cyan, magenta, yellow, and black inkjet inks are mixed in varying ratios on the print medium. One disadvantage of using color inkjet inks to print a black and white image is that the black and white image retains a non-neutral hue due to the intense colors of the color inkjet inks. Oftentimes, this hue deviates as a function of ink density. For example, as the ink density increases, the hue deviation from neutral can drift from a bluish hue to a rosy hue. In addition, the resolution of the black and white image is not as high as a black and white photograph because individual dots of the color inkjet ink are sometimes visible, especially in light areas of the image.
High resolution black and white images are printed by applying dots of inkjet ink adjacent to one another to create the desired shades of black and gray. Dithering is a process that simulates shades of gray by printing various sizes and shapes of dots adjacent to one another. Dithering reduces the contrast between dots of different shades and creates a more natural look between adjacent dots. Halftoning is a process of printing black and white images by printing dots of various sizes in an ordered array, such as on a fixed grid.
While artists typically desire the black and white image to have a neutral tone, artists sometimes want the black and white image to have a warm, cool, or sepia tone. As used herein a “neutral tone” is a tone that lacks chroma. A “warm tone” has a red or pink color, a “cool tone” has a blue, purple, or green color, and a “sepia tone” has a brown or yellow color. These tones are used to create a different mood in black and white images. Some photographers enhance their silver halide images using darkroom processes, such as platinum development baths, to create black and white image tones that deviate from neutral.
It would be desirable to produce high quality black and white images having a desired neutral, warm, or cool tone without using expensive, time consuming, and environmentally unfriendly photographic techniques. In addition, it would be desirable to improve the graininess and pixilation in black and white images. It would also be desirable to provide gray inkjet inks that are consistent at any dilution. Furthermore, it would be desirable to provide black and white images that are not negatively affected by particular lighting conditions.